A 9-year-old girl learning to fire a submachine gun accidentally killed her instructor at a shooting range when the weapon recoiled over her shoulder, according to Arizona authorities. The instructor, 39-year-old Charles Vacca, died at a hospital Monday after he was shot in the head.

The weapon was an Uzi, an Israeli-made submachine gun that some experts said had way too much firepower to use when teaching a child.

Gun experts contacted by CNN Wednesday said it was preferable to teach young children to shoot with single-shot firearms rather than submachine guns, but added that some Uzi submachine guns can be modified to control the powerful recoil.

"It's always the supervision," said Greg Danas, president of Massachusetts-based G&G Firearms. "But you also have gun enthusiasts running businesses where they place firearms in the hands of the uninformed, whether they're nine-year-old kids who are not capable or adults. It all stems from gun enthusiasts running businesses that require a level of professionalism and education. The unexpected with firearms is something that's only learned through years of being a trainer, not a gun enthusiast."

Danas questioned why the instructor in Arizona was standing immediately to the left of the Uzi, which would have recoiled in that direction.

"It's an awful shame," he said. "He shouldn't have been to the left side of the gun... But that child should not have been shooting anything other than a single-shot firearm."

Danas, whose daughters are 11 and 13, said his girls learned to shoot when they were 4 years old, with a single-shot, .22-caliber pistol.

Greg Block, who runs California-based Self-Defense Firearms Training, said not only was the Uzi the wrong gun to use -- "That's not a kid's gun" -- but that instructors should stand to the rear and to the right of the shooter.

"He was literally in the line of fire," Block said of the instructor. "He did pretty much everything wrong and I don't like saying that because it cost the man his life."

Steven Howard, a Michigan-based gun expert who runs American Firearms & Munitions Consulting, said the clip on the submachine gun should not hold more than three rounds during instruction.

"Teaching people machine gun 101, even with adults, even with people going through military training, the first few times they shoot machine guns you don't have them shoot a full freaking clip," he said. "The thing begins to fire and it begins to jump and buck all over the place. Your first human instinct is for your hands to clamp down, and you clamp down on the trigger and if the thing has a 32-round magazine ... it starts spraying all over and people get killed."

KSBW asked its Facebook readers on Wednesday, "What's the youngest age a person should be before they learn how to shoot an Uzi?"

Read responses below:

Janell Saber - "How about never?"

Alan Jump - "Enlistment age."

Nikki Lugo Caprara - "I'm a believer in the 2nd Amendment. I believe that children should be taught to respect guns and have a realistic view of the carnage that can ensue if used destructively. I have one child that has taken gun safety courses, hunter safety, and has spent many hours on the range with a qualified adult. For the life of me, I see no common sense reason why my 13 year old should be shooting an Uzi. I'm not sending him off to war next week or next year."

Mike Santos - "This young girl will have this horrible memory for the rest of her life, as well as both families."

Justine Myers - "It depends on the gun and the situation. I let my 11 year old son shoot an AR-15 and I was so proud. He understands the danger of guns and respects gun safety. I believe the more they're informed the better they will handle a gun. I think every child should go through gun safety courses."

Adam Niehuser - "A 9 year old with a automatic weapon, what could possible go wrong."

Jennifer Banchero Olds - "There is no reason for these guns to be in the hands of anyone but a trained soldier! Now a man is dead and a little girl is likely traumatized for life! And I'm sure there are a lot of gun fanatics who don't see anything wrong with this picture."

James Anderson Merritt - "No extremely powerful firearm should be the first thing that a child learns to use. It is best to work up from 22s or even BB-guns. I started my son on 22s when he was about the girl's age. After a while, he wanted to try something bigger, so we gave that a go. He handled himself well but felt the difference in recoil kick and heard the difference in report; he understood that he'd have to brace himself every time he upgraded to a more powerful weapon."

Robert Coble - "Stupid question. No one should be shooting an Uzi."

Jessica Urioste Marquez - "Parents fault completely! Now this little girl has to spend the rest of her life knowing that she killed someone!"